Microelectronic devices, such as semiconductor devices, are generally fabricated on and/or in wafers or workpieces. A typical wafer plating process involves depositing a seed layer onto the surface of the wafer via vapor deposition. A photoresist may be deposited and patterned to expose the seed. The wafer is then moved into an electroplating processor where electric current is conducted through an electrolyte to the wafer, to apply a blanket layer or patterned layer of a metal or other conductive material onto the seed layer. Examples of conductive materials include permalloy, gold, silver, copper, and tin. Subsequent processing steps form components, contacts and/or conductive lines on the wafer.
In some electroplating processors, a current thief electrode is used to better control the plating thickness at the edge of the wafer and for control of the terminal effect on thin seed layers. The terminal effect for a given seed layer increases as the electrical conductivity of the electrolyte bath increases. Hence, a current thief electrode can be effectively used with thinner seed layers combined with high conductivity electrolyte baths. The use of thin seed layers is increasingly common with redistribution layer (RDL) and wafer level packaging (WLP) plated wafers.
Uniformity of electroplated materials across the wafer is important and becomes more and more important as device characteristic dimensions shrink and/or wafers increase in size. Accordingly, engineering challenges remain in designing apparatus and methods for electroplating wafers, and other applications, using a thief electrode.